U.S. patent number 5,713,576 [Application Number 08/314,675] was granted by the patent office on 1998-02-03 for gas lubricated barrier seal.
This patent grant is currently assigned to John Crane Inc.. Invention is credited to James P. Netzel, Douglas J. Volden, James R. Wasser.
United States Patent |
5,713,576 |
Wasser , et al. |
February 3, 1998 |
Gas lubricated barrier seal
Abstract
A double, back to back oriented mechanical end face seal
arrangement for use in sealing pumps or other devices used in fluid
transfer of toxic or corrosive fluid has an intermediate buffer
fluid chamber into which a relatively inert gas, such as nitrogen,
is provided for use as a buffer fluid, and is maintained at a
pressure which exceeds the process fluid pressure by at least 10
p.s.i. Each seal has a primary ring and a mating ring with gap
maintaining means, such as spiral pumping grooves, formed in one of
the rings which are shaped and dimensioned to pump the buffer gas
through the first seal from the intermediate chamber into the
process fluid chamber against the process fluid pressure and
through the second seal from the intermediate chamber into the
environment external to the housing and sealing area, thus avoiding
the escape of the process fluid into the intermediate buffer
chamber and thereby to the atmosphere. The inboard seal includes a
first secondary sealing means disposed between one seal ring and
the housing for sealing therebetween and a second secondary sealing
means, disposed between the other seal ring and the shaft for
sealing therebetween, the first and second secondary sealing means,
which may comprise O-rings, each defining the boundary between the
intermediate chamber and the process fluid chamber. The first and
second secondary sealing means of the first rotary mechanical end
face seal are sized and disposed to define radial walls in the back
radial surfaces of each seal ring to thereby present essentially an
equal area at an approximately identical radius, such that
essentially the same mount of buffer fluid pressure acts on the
back radial surfaces of each ring of the first rotary mechanical
and face seal but in opposite directions and, on the process fluid
side, the identical process fluid pressure acts on opposite sides
of a portion of the respective rings of the first rotary mechanical
end face seal essentially eliminating thrust forces acting on the
first rotary mechanical end face seal.
Inventors: |
Wasser; James R. (Des Plaines,
IL), Volden; Douglas J. (Park Ridge, IL), Netzel; James
P. (Skokie, IL) |
Assignee: |
John Crane Inc. (Morton Grove,
IL)
|
Family
ID: |
25485177 |
Appl.
No.: |
08/314,675 |
Filed: |
September 29, 1994 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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946914 |
Sep 18, 1992 |
5375853 |
|
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Current U.S.
Class: |
277/304; 277/306;
277/408; 277/431; 277/400; 277/348; 277/927 |
Current CPC
Class: |
F16J
15/3412 (20130101); F16J 15/3404 (20130101); F16J
15/406 (20130101); Y10S 277/927 (20130101) |
Current International
Class: |
F16J
15/40 (20060101); F16J 15/34 (20060101); F16J
015/38 () |
Field of
Search: |
;277/96,96.1,96.2,59,65,27,1,81R,3,17,85,38 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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297381 |
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Jul 1989 |
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EP |
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2030133 |
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Dec 1971 |
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DE |
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2444544 |
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Jan 1976 |
|
DE |
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3819566 |
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Dec 1989 |
|
DE |
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755955 |
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Sep 1975 |
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ZA |
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2234788 |
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Feb 1991 |
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GB |
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Other References
John Crane Inc. Drawing No. H-SP-11505, Dated Oct. 11, 1990,
Publication or sale date: 1991. .
John Crane Inc. Drawing No. H-SP-12582-1, Dated Oct. 11, 1990,
publication or sale date: 1991. .
John Crane Inc. Drawing No. H-SP-10979, date May 2, 1990. .
Double-bellows seal non-contacting, Chemical Processing Magazine,
p. 33, author unavailable, Sep. 1997. .
Dulak, J.J., "Sealing Hazardous Gas" Reprinted from Machine Design,
Mar. 8, 1990 issue, 2 pages. .
Netzel, J. "Sealing systems keep pace with the times", Reprint from
PEM Plant Engineering and Maintenance, Jan. 1989 issue, 4 pages.
.
Bulletin entitled "John Crane Type 28 Series Dry-Running Gas Seals"
John Crane Inc. Indicated copyright date of: 1989. .
Shah. P. "Dry Gas Compressor Seals" Published in the Proceedings of
the 17th Turbomachinery Symposium, Nov. 1988. .
Gabriel, R., "Fundamentals of Spiral Groove Noncontacting Face
Seals" orginally presented at the Annual Meeting of Lubrication
Engineers, Apr., 1978., 36 pages. .
Brochure B2.539V Cranpac GmbH, publ. May 1985. .
Brochure B1.501V Cranpac GmbH, publ. Apr. 1985. .
"Compressor Seal Oil Systems", J. Read The South African Mechanical
Engineer, vol. 39, Apr. 1989, pp. 176,180. .
"Recent Developments on Non-Contacting Face Seals", J. Gardner,
American Society of Lubrication Engineers, May, 1973. .
"Dry Running Seal Technology", P. Wilde, John Crane, Inc., Apr.
1983. .
"Upstream Pumping: New Developments in Mechanical Seal Design",
Afzal Ali, John Crane, Inc. Apr. 1989. .
"Gas Lubricated Mechanical Seals and Their Gas Supply Systems for
Compressors", R. Kollinger, Burgmann. .
Application Mechanical Seals, "Seal Technology, A Control for
Industrial Pollution", J. Netzel, The Reporter, vol. I, Summer
Issue 1991. .
"Sealing Solutions", J. Netzel, Plant Engineering and Maintenance,
Mar. 1991..
|
Primary Examiner: DePumpo; Daniel G.
Attorney, Agent or Firm: Dorn, McEachran, Jambor &
Keating
Parent Case Text
This is a continuation of application Ser. No. 07/946,914, filed on
Sep. 18, 1992, now U.S. Pat. No. 5,375,853.
Claims
What is claimed is:
1. A method for sealing against leakage of process fluid under
pressure within a housing along a rotatable shaft extending through
a wall of the housing, said method comprising the steps of:
utilizing a seal arrangement having:
a first rotary mechanical end face seal including a stationary seal
ring for sealing connection to the housing and a rotary seal ring
for sealing connection to the shaft, each said ring having radial
surfaces, and each said ring including an annular generally
radially extending sealing face, being coextensive with one of said
radial surfaces spaced from at least one other of said radial
surfaces thereof, and in relatively rotating, mating sealing
relation with the sealing face of the other of said rings, one of
said seal rings being axially movable relative to the other;
a second rotary mechanical end face seal including a stationary
seal ring for sealing connection to the housing and a rotary seal
ring for sealing connection to the shaft, each said ring having an
annular generally radially extending sealing face in relatively
rotating, mating sealing relation with the face of the other of
said rings, one of said seal rings of said second rotary mechanical
end face seal being axially movable relative to the other said seal
ring independently of the axial movement of the axially moveable
ring of said first rotary mechanical end face seal;
said first and second rotary mechanical end face seals including
means directly biasing each of the axially moveable rings toward
its associated stationary ring to maintain said annular sealing
face of said axially moveable ring in said relatively rotating
sealing relation to said annular sealing face of said stationary
ring;
said first and second rotary mechanical end face seals being
axially spaced apart along the shaft and arranged to define, with
said housing, an intermediate chamber therebetween;
the relatively rotatable seal rings of said first rotary mechanical
end face seal having a first annular circumference of said sealing
faces exposed to the process fluid to be sealed within the housing,
and a second annular circumference of said sealing faces exposed to
said intermediate chamber;
the relatively rotatable seal rings of said second rotary
mechanical end face seal having a first annular circumference of
said sealing faces exposed to said intermediate chamber, and a
second annular circumference of said sealing faces exposed to the
ambient environment external to said housing;
said intermediate chamber including means for connection to a
source of relatively inert gas barrier fluid at a gas barrier fluid
pressure exceeding the pressure of said process fluid present at
said annular seal face first circumference of said first rotary
mechanical end face seal rings;
said first rotary mechanical end face seal including
gap-maintaining means to cause said seal to operate, during shaft
rotation, as a gas lubricated, non-contacting seal in the presence
of said gas barrier fluid at said gas barrier fluid pressure;
and
said first rotary mechanical end face seal further including means
to cause said seal to operate, during shaft rotation, as a
contacting seal in the absence of said gas barrier fluid
pressure;
supplying a relatively inert gas barrier fluid to said intermediate
chamber at a gas barrier fluid pressure exceeding the pressure of
said process fluid present at said annular seal face first
circumference of said first rotary mechanical end face seal
rings;
operating said first rotary mechanical end face seal, during shaft
rotation, in the presence of said gas barrier fluid pressure as a
gas lubricated, non-contacting seal, and essentially eliminating
thrust forces acting on said first rotary mechanical end face seal,
by providing said first rotary mechanical end face seal with a
first secondary sealing means disposed between one of said seal
rings and the housing for providing a sealing connection
therebetween and a second secondary sealing means disposed between
the other seal ring and the shaft for providing a sealing
connection therebetween, to define the boundary between said
intermediate chamber and said process fluid within said housing,
and sizing and disposing said first and second secondary sealing
means of said first rotary mechanical end face seal to define
radial walls in said other radial surfaces and thereby presenting
essentially an equal area at an approximately identical radius,
such that the essentially same amount of buffer fluid pressure acts
on the radial surfaces of each of said rings of said first rotary
mechanical end face seal but in opposite directions and on the
process fluid side, the identical process fluid pressure thereby
acting on opposite sides of a portion of each of said respective
rings of said first rotary mechanical end face seal to essentially
eliminate thrust forces acting on said first rotary mechanical end
face seal.
2. A method as claimed in claim 1 wherein said source of relatively
inert gas supplies to the intermediate chamber a relatively inert
gas which comprises at least one gas taken from the group of
nitrogen, carbon dioxide, air or one of the noble gases.
3. A method as claimed in claim 1 wherein said first and second
mechanical end face seals are provided preassembled together as a
cartridge and are installed as a unit.
4. A seal arrangement for sealing against leakage of process fluid
under pressure within a housing process fluid chamber along a
rotatable shaft extending through a wall of the housing, said seal
arrangement comprising:
a first rotary mechanical end face seal including a stationary seal
ring for sealing connection to the housing and a rotary seal ring
for sealing connection to the shaft, each said ring having a radial
surface including an annular generally radially extending sealing
face and at least one other radial surface, said sealing face
spaced from the other of said radial surfaces thereof, and said
sealing face being in relatively rotating, mating sealing relation
with the sealing face of the other of said rings, one of said rings
being axially moveable relative to the other;
a second rotary mechanical end face seal including a stationary
seal ring for sealing connection to the housing and a rotary seal
ring for sealing connection to the shaft, each said ring having an
annular generally radially extending sealing face in relatively
rotating, mating sealing relation with the face of the other of
said rings, one of said seal rings being axially movable relative
to the other said seal ring independently of the axially moveable
ring of said first rotary mechanical end face seal;
said first and second rotary mechanical end face seals including
means directly biasing each of the axially moveable rings toward
its associated stationary ring to maintain said annular sealing
face of said axially moveable ring in said relatively rotating
sealing relation with said annular sealing face of said stationary
ring;
said first and second rotary mechanical end face seals being
axially spaced apart along the shaft and arranged to define, with
said housing, an intermediate chamber therebetween;
the relatively rotatable seal rings of said first rotary mechanical
end face seal having a first annular circumference of said sealing
faces exposed to the process fluid to be sealed within the housing
process fluid chamber, and a second annular circumference of said
sealing faces exposed to said intermediate chamber;
the relatively rotatable seal rings Of said second rotary
mechanical end face seal having a first annular circumference of
said sealing faces exposed to said intermediate chamber, and a
second annular circumference of said sealing faces exposed to the
ambient environment external to said housing;
said intermediate chamber including means for connection to a
source of relatively inert buffer gas at a pressure exceeding the
pressure of said process fluid present at said circumference of
said sealing faces exposed to the process fluid;
said first rotary mechanical end face seal including gap
maintaining means defined by said relatively rotating sealing faces
to maintain said seal faces at a gap during shaft rotation in the
presence of said buffer gas at said pressure exceeding the pressure
of said process fluid present at said circumference of said sealing
faces exposed thereto;
said first rotary mechanical end face seal further including a
first secondary sealing means disposed between one of said seal
rings and the housing for sealing therebetween and a second
secondary sealing means disposed between the other of said seal
rings and the shaft for sealing therebetween, said first and second
secondary sealing means each defining the boundary between said
intermediate chamber and said process fluid chamber, said first and
second secondary sealing means of said first rotary mechanical end
face seal being sized and disposed to define radial walls in said
other radial surfaces to thereby present essentially an equal area
at an approximately identical radius, such that essentially the
same amount of buffer fluid pressure acts on said other radial
surfaces of each of said rings of said first rotary mechanical end
face seal but in opposite directions and, on the process fluid
side, the identical process fluid pressure acts on opposite sides
of a portion of said respective rings of said first rotary
mechanical end face seal essentially eliminating thrust forces
acting on said first rotary mechanical end face seal.
5. The seal arrangement as claimed in claim 4 wherein said first
and second secondary sealing means include an O-ring disposed in
sealing relation between said stationary seal ring and one of said
housing and shaft and an O-ring disposed in sealing relation
between said rotary seal ring and the other of said housing and
shaft.
6. The seal arrangement as claimed in claim 5 wherein said gap
maintaining means comprises a plurality of grooves formed on one of
said relatively rotating sealing faces extending from said
circumference exposed to said intermediate chamber toward said
other circumference, said one of said relatively rotating sealing
faces further defining a sealing dam between said grooves and said
other circumference.
7. The seal arrangement as claimed in claim 6 wherein said grooves
are spiral grooves.
8. The seal arrangement as claimed in claim 5 wherein said
secondary sealing means associated with said axially moveable seal
ring includes a radial wall associated with said one of said shaft
and housing, said radial wall being in fixed axial position and
disposed adjacent said O-ring in sealing relation between said
axially moveable ring and said one of said shaft and housing.
9. The seal arrangement as claimed in claim 6 wherein said
secondary sealing means associated with said axially moveable seal
ring includes a radial wall associated with said one of said shaft
and housing, said radial wall being in fixed axial position and
disposed adjacent said O-ring in sealing relation between said
axially moveable ring and said one of said shaft and housing.
10. The seal arrangement as claimed in claim 7 wherein said
secondary sealing means associated with said axially moveable seal
ring includes a radial wall associated with said one of said shaft
and housing, said radial wall being in fixed axial position and
disposed adjacent said O-ring in sealing relation between said
axially moveable ring and said one of said shaft and housing.
11. The seal arrangement of claim 4 said axially moveable ring of
said first rotary mechanical end face seal further includes a
radially extending surface spaced from said radial sealing face,
said surface being exposed to the pressure of the process fluid in
said process fluid chamber.
12. The seal arrangement of claim 5 said axially moveable ring of
said first rotary mechanical end face seal further includes a
radially extending surface spaced from said radial sealing face,
said surface being exposed to the pressure of the process fluid in
said process fluid chamber.
13. The seal arrangement of claim 6 said axially moveable ring of
said first rotary mechanical end face seal further includes a
radially extending surface spaced from said radial sealing face,
said surface being exposed to the pressure of the process fluid in
said process fluid chamber.
14. The seal arrangement of claim 7 said axially moveable ring of
said first rotary mechanical end face seal further includes a
radially extending surface spaced from said radial sealing face,
said surface being exposed to the pressure of the process fluid in
said process fluid chamber.
15. The seal arrangement of claim 8 said axially moveable ring of
said first rotary mechanical end face seal further includes a
radially extending surface spaced from said radial sealing face,
said surface being exposed to the pressure of the process fluid in
said process fluid chamber.
16. The seal arrangement of claim 8 said axially moveable ring of
said first rotary mechanical end face seal further includes a
radially extending surface spaced from said radial sealing face,
said surface being exposed to the pressure of the process fluid in
said process fluid chamber.
17. The seal arrangement of claim 10 said axially moveable ring of
said first rotary mechanical end face seal further includes a
radially extending surface spaced from said radial sealing face,
said surface being exposed to the pressure of the process fluid in
said process fluid chamber.
18. A seal arrangement as claimed in claim 4 wherein said
relatively inert gas is taken from the group consisting of
nitrogen, carbon dioxide, air and a noble gas.
19. A seal arrangement as claimed in claim 4 wherein said gap
maintaining means on the seal face of one of said rings of said
first rotary mechanical end face seal are formed on said stationary
seal ring.
20. A seal arrangement as claimed in claim 19 wherein said
stationary seal ring sealed against the housing of said first
rotary mechanical end face seal is a mating ring and said rotary
seal ring sealed against said shaft is an axially moveable primary
ring which is biased by said biasing means.
21. A seal arrangement as claimed in claim 6 wherein said grooves
on the seal face of one of said rings of said first rotary
mechanical end face seal extend from the outer diameter toward the
inner diameter of said seal ring face and the dam is adjacent the
inner diameter of said seal ring face.
22. The seal arrangement of claim 4 further comprising a sleeve
sealingly connected to said shaft, said sleeve being disposed
between said shaft and said axially moveable ring of said first
rotary mechanical end face seal, said axially moveable ring being
disposed around said sleeve, said axially moveable ring rotating
with said shaft and said sleeve, one of said second secondary
sealing means providing a seal between a cylindrical surface of
said axially moveable ring and said sleeve while permitting axial
movement of said axially moveable ring relative to said sleeve, and
said seal arrangement including at least one radially extending
secondary seal wall retained in fixed axial position relative to
said sleeve.
23. A seal arrangement as claimed in claim 22 wherein said first
and second seals are preassembled as a cartridge for
installation.
24. A seal arrangement as claimed in claim 23 wherein said means
biasing each of the axially moveable rings toward the other for
each of said first and second rotary mechanical end face seals
comprises a common spring which biases each of the axially moveable
rings outwardly from a location central to both of said axially
moveable rings.
25. A seal arrangement as claimed in claim 21, wherein the radial
face of one of said rings of said second rotary mechanical end face
seal includes a plurality of grooves extending from said
circumference exposed to said intermediate chamber partially toward
said circumference exposed to the ambient environment external to
said housing and defining an annular dam adjacent said
circumference exposed to the ambient environment external to said
housing.
26. A seal arrangement as claimed in claim 25 wherein said grooves
on the seal face of one of said rings of said second rotary
mechanical end face seal extend from the outer diameter toward the
inner diameter of said seal ring face and the dam is adjacent the
inner diameter of said seal ring face.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to mechanical end face
seals and more particularly relates to dual mechanical end face
seals for use in sealing toxic or corrosive fluids.
2. Background Art
Mechanical end face seals have long been used to seal the space
between a housing and a relatively rotating shaft which passes
through the housing. Such seals usually include a primary ring
which has a generally planar radial sealing face and is fixed to
and mounted in the housing. The primary ring may be mounted on the
housing by a secondary seal, such as an O-ring. In addition, the
seal includes a mating ring which is mounted on the shaft for
rotation therewith. Like the primary ring, the mating ring has a
generally planar radial sealing surface. The mating ring radial
surface is disposed in opposing relationship to the primary ring
and the two radial surfaces are biased into sealing engagement.
These types of seals are described in U.S. Pat. No. 4,212,475
issued to J. Sedy and assigned to the same assignee as the present
invention.
Many configurations are known for utilizing either a single seal or
a plurality of mechanical end face seals used together for specific
seal applications. Single seal configurations are adequate for most
sealing applications, including pumps, compressors, mixers and the
like when utilized to seal fluids which are benign with respect to
the environment. More recently, however, rising concern over
pollution and toxic emissions has culminated in regulatory
directives calling for "zero emissions" of toxic fluids into the
environment. Thus, a need has arisen in the seal industry for seals
which can provide a solution to the toxic fluid emission problem.
Possible solutions which approached or met the zero emission
standard have been proposed. These proposals have resulted in two
broad categories of seal design, one type being known as "wet"
double seals and the other type being magnetic drive pumps.
An example of the "wet" seals can be found in U.S. Pat. No.
4,290,611, issued to J. Sedy and also assigned with the present
invention to a common assignee. That patent describes and
illustrates a "double seal" arrangement (FIG. 1) which utilizes two
mechanical and face seals oriented back to back along a drive
shaft. The two seals define a chamber between them into which a
lubricant buffer fluid is continuously circulated for cooling the
seal rings. The buffer fluid, usually oil, is at a pressure
generally 5-20 p.s.i. above the sealed process fluid pressure. The
arrangement is described as being most desirable for sealing
corrosive liquids because the metal parts of the seal are isolated
from the process fluid by use of a non-corrosive buffer liquid.
The seal arrangements described in the '611 patent work well in
certain applications, but cannot be used in applications where the
sealed process fluid is a gas or where the sealed fluid is a liquid
in which contamination by the buffer fluid cannot be tolerated.
Generally, oil is used as a buffer fluid but many process fluids
are reactive with the oil, or contamination by the oil in the
process fluid is not desirable.
More recently, magnetic drive pumps have been developed which
provide a "zero emission" capability, albeit at greater expense.
For these types of applications, the shaft does not extend through
the housing, but the shaft terminates at the housing wall thus
eliminating the opening through which the shaft would extend. The
impeller which pumps the fluid is encased in the housing chamber
and is connected to a first set of magnets. The impeller is driven
by a second set of magnets which are disposed externally of the
chamber. Rotation of the externally disposed magnets by an external
motor, in turn, rotates the magnets connected to the impeller
inside the encasing housing chamber. Since the housing chamber is
completely encased and does not include a shaft opening, no leakage
of fluid can take place through the chamber wall under normal
operating conditions.
The magnetic drive pumps are more complex and expensive than
conventional mechanical end face seals. The magnets which drive the
impeller are of special construction and special bearings are
necessary to maintain the alignment of the magnets and the impeller
shaft which provides the connection to the impeller. Moreover,
magnetically driven pumps require a coolant fluid stream to remove
waste heat generated by magnetic losses and by friction.
What is required by the industry is an inexpensive, easily
constructed, seal which has a "zero emission" capability and which
meets the regulations for toxic fluid emissions in an increasingly
regulatory environment for general use.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides for a seal arrangement
for sealing against leakage of process fluid under pressure within
a housing along a rotatable shaft extending through a wall of the
housing, the seal arrangement generally comprising a first rotary
mechanical end face seal including a stationary seal ring for
sealing connection to the housing and a rotary seal ring for
sealing connection to the shaft, each ring having an annular
generally radial sealing face in relatively rotating, mating
sealing relation with the face of the other ring, a second rotary
mechanical end face seal including a stationary seal ring for
sealing connection to the housing and a rotary seal ring for
sealing connection to the shaft, each ring having an annular
generally radial sealing face in relatively rotating, mating
sealing relation with the face of the other of the rings, the first
and second rotary mechanical end face seals being axially spaced
along the shaft and arranged to define, with the housing, an
intermediate chamber therebetween, each seal including means
biasing one of the rings toward the other to maintain the annular
sealing faces of each seal ring in relatively rotating sealing
relation the relatively rotatable sealing rings of the first end
face seal having one annular circumference of the sealing faces
exposed to the process fluid to be sealed within the housing, and
the other annular circumference of the sealing faces exposed to the
intermediate chamber, the relatively rotatable sealing rings of the
second seal having one annular circumference of the sealing faces
exposed to the intermediate chamber, and the other annular
circumference of the sealing faces exposed to the ambient
environment external the housing, the intermediate chamber being in
communication with the interior of the housing containing process
fluid under pressure only across the relatively rotating, mating,
sealing faces of the first rotary mechanical end face seal, the
intermediate chamber being in communication with the ambient
environment external to the housing only across the relatively
rotating, mating, sealing faces of the second rotary mechanical end
face seal, the intermediate chamber including means for connection
to a source of relatively inert gas at a pressure exceeding the
pressure of the process fluid present at the circumference of the
annular seal faces of the first rotary mechanical end face seal
rings.
In one embodiment of the invention, the radial face of one of the
rings of the first rotary mechanical end face seal includes a
plurality of spiral grooves extending from the circumference
exposed to the relatively inert gas in the intermediate chamber,
which may be the outer circumferential diameter of the seal rings,
partially toward the circumference exposed to the process fluid in
the interior of the housing, which may be the inner circumferential
diameter, and defining on the face an annular dam adjacent the
circumference exposed to the process fluid in the housing, or the
outer circumferential diameter. The primary rings of both seals in
the preferred form rotate together with the shaft. The preferable
buffer gas is nitrogen.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross section, axially, of a housing and shaft
incorporating a preferred embodiment of the invention.
FIG. 2 is an end view of one of the sealing rings of the preferred
embodiment of the invention.
FIG. 3 is an end view of the other of the sealing rings of the
preferred embodiment of the invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT
FIG. 1 illustrates a seal generally indicated at 10 constructed in
accordance with the preferred embodiment of the present invention.
The seal is designed to seal toxic fluids within a housing 12 so
that literally "zero emission" of the sealed toxic process fluid is
achieved and literally no process fluid escapes to the ambient
environment external to the housing. The housing includes a shaft
passage 14 which affords a shaft 16 to extend through the housing
12. The housing 12 may comprise a stuffing box, such as has used in
the past for the stuffing of packing, the packing having been
pressed against the shaft to minimize leakage through the housing
and shaft interface. The housing 12 further separates an inner
chamber 18 containing process fluid from the ambient environment 20
external the housing which generally comprises the atmosphere.
The seal arrangement of the preferred embodiment is disposed
adjacent the housing 12 and generally within the stuffing box
formed by the housing 12. A seal arrangement including double, back
to back oriented, axially-spaced rotary, mechanical end face seals
of the spiral groove type each have opposed ring portions
respectively secured to the housing 12 and shaft 16. The seals are
similar in most respects to the type shown and described in
aforementioned U.S. Pat. No. 4,212,475.
The seal arrangement comprises a first seal, generally indicated at
22, adjacent the process fluid chamber 18 and enclosed by the wall
of housing 12, and a second seal 24 adjacent the ambient
environment 20 external to the seal arrangement and to the housing.
The first and second seals 22 and 24 define an intermediate chamber
26 between them. The chamber 26 is surrounded by a liner assembly
28, which together with a flanged gland plate 30, define the other
end wall of the intermediate chamber 26. The shaft 16 includes a
sleeve assembly 32 which surrounds the shaft and which is a base on
which the seal rings rest and around which the seals 22, 24 are
disposed.
The first seal 22 includes a pair of annular rings comprising a
rotating seal ring 36 and a stationary seal ring 40. Rotating seal
ring 36 has a radially extending face 38 and a radially extending
shoulder 37 disposed at the outer circumference. The rotating seal
ring 36 is opposed to the stationary seal ring 40 having a radially
extending face 42 opposite the face 38 of the rotating ring 36. The
stationary seal ring 40 is also referred to herein as the mating
ring 40 and the rotating seal ring 36 is also referred to herein as
the primary ring 36. As will be described below, this relationship
is not the only configuration of the seal rings possible in
practicing the present invention. The primary ring 36 shown in the
preferred embodiment is fixed relative to the shaft 16 and rotates
therewith. The primary ring 36 is sealed against the sleeve 32, but
is shaped and dimensioned to have freedom of motion axially
relative to the sleeve 32 and shaft 16 at least to a limited
degree.
As shown in FIG. 1, the primary ring 36 is fixed in the rotational
direction relative to the sleeve assembly 32 for rotation
therewith. However, it is possible in an alternative embodiment
(not shown) to have the primary ring fixed relative to the housing,
and the mating ring to be rotating with the shaft. In that
embodiment, suitable modification of the arrangement within the
skill of a person knowledgeable in the art would be necessary to
accommodate such an alternative design.
The mating ring 40 has a face 42 in facing relation to face 38 of
the primary ring 36. When they are brought together, the faces 38
and 42 interface and provide the sealing function of the seal 22.
The interface need not be co-extensive with both of the faces 38
and 42, but as is shown in FIG. 1, the face 38 of the primary ring
36 extends only part way across the face 42 of the mating ring
40.
The interface between faces 36 and 42 is in the shape of an annular
disc, with the shaft 16 extending through the central aperture of
each ring. As shown in FIG. 2, the mating ring 40 includes a
plurality of spiral grooves 44 disposed partially across the face
42 of ring 40, and extending from the outer circumferential
diameter toward the inner circumferential diameter thereof. The
grooves 44 are also illustrated in phantom in FIG. 1 but the depth
of the grooves is exaggerated for illustrative convenience. As is
described in aforementioned U.S. Pat. No. 4,212,475, the depth of
the grooves is on the order of 50 to about 400 microinches. In the
preferred embodiment, the grooves are about 300 microinches in
depth.
Referring to FIG. 2, grooves 44 are circumferentially and evenly
spaced and are separated by plural radially extending lands 45. An
ungrooved surface at the inner diameter of seal face 42 defines a
sealing dam 46 which, in cooperation with the opposed face 38 of
the primary seal ring 36, provides a static seal when the shaft 16
is not rotating. When shaft 16 is not rotating, the process fluid
is sealed by a hydrostatic film between the primary and mating
rings at the sealing dam 46. When the shaft starts rotating,
interaction of the grooves 44 with the rotating face 38 of ring 36
normally pumps a fluid present in the chamber 26 radially inwardly
across the seal faces 38, 42, causing the seal faces to open
slightly to present a gap between the faces. The fluid which is
pumped into the gap maintains a non-contacting condition between
the seal faces and also acts to cool the faces of excess heat which
is generated by shear frictional forces of the relatively rotating
seal faces.
At the end of the mating ring 40 opposite from that of the face 42,
(FIG. 1), there is a depression or bore 41 which is disposed to
receive a retainer pin 43 to fix ring 40 relative to the liner
assembly 28 and to the housing 12. The retainer pin is generally an
element of the liner assembly 28 and may be an integral element
which is machined as a portion of the assembly. Preferably, the
retainer pin 43 is a separate element which is press fitted into
the liner during manufacture. An O-ring 47 is used to seal the
mating ring 40 to the liner assembly 28. A shoulder in the outer
circumferential wall of the primary ring 40 provides for a radially
extending annular wall 39 which abuts a corresponding radially
extending wall of the liner assembly.
The seal 22 is shown having the grooves 44 at the radially outer
diameter adjacent the intermediate chamber 26 and the sealing dam
46 at the radially inner diameter adjacent to and being exposed to
the process fluid within the chamber 18. The principles of the
invention, however, are applicable to seals having the grooves at
the inner diameter and the dam at the outer diameter, with the
inner diameter grooves being exposed to the buffer fluid within the
intermediate chamber. Such an alternate embodiment (not shown) may
require a different configuration of the rings, e.g., with the
mating ring rotating and the primary ring stationary. It is within
the skill of those in the art to design an alternative
configuration with the stated characteristics upon achieving an
understanding of the present invention.
The sleeve assembly 32 includes a shaft sleeve 48 which fits upon
the shaft 16. Sleeve 48 includes a thicker portion 50 at one end,
which is recessed to provide a thinner portion 51 at the other
annular end of the sleeve 48. The sleeve 48 is fixed to the shaft
16 by a collar 52 secured to the thinner portion 51 of sleeve 50 by
a bolt, as will be explained below. Alternatively, a drive key
arrangement (not shown) may be used to secure shaft sleeve 48 to
the shaft 16. Sleeve assembly 32 further includes an O-ring 56 for
sealing between the thicker portion 50 and the shaft 16, and
another O-ring 58 for sealing between the primary ring 36 and the
thicker portion 50. The recessed thinner portion 51 of sleeve 48
accommodates assembly of other portions of the seal arrangement,
such as the elements of the second seal 24.
The O-rings 56 and 58 are fit into appropriate grooves in the
thicker portion 50, and the outer diameter O-ring 58 is shaped,
sized and configured to permit axial motion of the primary ring 36.
The O-ring 58 is of a diameter as close as possible to the diameter
of O-ring 47. O-rings of the same diameter enhances seal balance of
the seal 22 because it tends to equalize the forces which arise
from the process fluid pressure which is present in chamber 18. The
O-rings set the radial location of the boundary between the
pressure of the buffer fluid and of the process fluid, as will be
explained below. The O-rings 47,58 thus define the balanced
pressure acting on radially extending surfaces of each of the seal
rings 36 and 40. The higher pressure buffer fluid acts on the
radially extending walls 39 of seal ring 40 while a simultaneous
and opposite force acts on the face of the seal ring 36 which is
opposite the seal ring 36 from the face 38. Because the annular
widths in the radial direction of the wall 39 and the
non-contacting radial face of ring 36 present essentially an equal
area at an approximately identical radius, essentially the same
amount of buffer fluid pressure acts on each of the rings albeit in
the opposite directions. On the process fluid side, the identical
process fluid pressure acts on opposite sides of a portion of
mating ring 40 and on a portion of primary ring 36. Thus, the
pressure forces on each of the rings cancel each other out, thereby
essentially eliminating thrust forces acting on the seal 22.
Seal 24 also includes a pair of annular rings. One ring comprises a
stationary ring 60 having a radially extending face 62. The
stationary seal ring 60 is opposed to the other ring, rotating ring
64, also having a radially extending face 66 opposite the face 62
of stationary ring 60. The stationary seal ring 60 of second seal
24 is also referred to as the mating ring seal 60 and the rotating
seal ring 64 is also referred to as the primary seal ring 64.
Primary seal ring 64 is not identical in construction to the ring
36. For example, a recessed groove 68 in the primary seal ring end
opposite the seal face 66 provides accommodation for an O-ring 70
which seals between the ring 64 and the thicker portion 50 of the
sleeve 48. In many respects, including the disposition of the
O-ring 70, the second seal 24 is similar to the seal described and
illustrated in aforementioned U.S. Pat. No. 4,212,475. In one
important respect, however, seal 36 is different from that of the
seal described in that patent. The disclosure in the '475 patent
describes the primary ring fixed to the housing within a retainer.
However, in the preferred embodiment of the present invention, the
primary ring 64 is rotating and the mating ring 60 is stationary.
Different design considerations are applicable in either case. For
example, the retainer of the seal in the patent includes an
elongated inner diameter wall on which an O-ring seals against the
primary ring whereas in the present invention, the corresponding
O-ring 70 rests on the sleeve 48. Nevertheless, the teaching of the
present invention is applicable to seal configurations having any
of a number of designs which may be within the purview of those
having ordinary skill in the art.
Referring again to FIG. 1, a shoulder in the outer circumferential
wall of the primary ring 64 provides for a radially extending
annular wall 72.
The mating ring 60 of seal 24 is also different from that of mating
ring 40. Mating ring 60 is an annular ring with an annular groove
77 disposed in the outer circumference for receiving an O-ring 75.
The O-ring 75 provides a seal between mating ring 60 and gland
plate 30.
Referring to FIG. 3, where an elevation view of the seal face 62 of
ring 60 is illustrated, seal face 62 also includes a plurality of
circumferentially spaced spiral grooves 74. The grooves extend
partially across the radial width of mating ring seal face 62 and
are also shown in mating ring 60 of FIG. 1, the width being
exaggerated for illustrative convenience. An ungrooved surface at
the inner diameter of seal face 62 defines a sealing dam 76 which,
in cooperation with the opposed sealing face 66 of the primary ring
64, provides a static seal when the shaft 16 is not rotating,
similar to the dam 46 of seal 22. During shaft rotation, the shaft
16 and primary ring 64 rotate relative to the mating ring 60 and
the interaction of the rotating face 66 of primary ring 64 and the
spiral grooves 74 in seal face 62 acts to pump the buffer fluid
within intermediate chamber 26 across the seal interface of seal 24
and into the ambient environment 20.
Utilization of stationary mating rings 40, 60 together with the
faces 42, 62 including the spiral grooves 44, 74 respectively, is
the reverse of most seal designs. It has been found, however, that
whether the rings having the spiral grooves are disposed on a
rotating ring, as in the seal described in aforementioned U.S. Pat.
No. 4,212,475, or whether the rings having the grooves are
maintained stationary, as in the present invention, does not
provide an appreciable difference in the amount or direction of the
pumping action on the fluid.
It is believed that a film of fluid rides together with the
rotating ring, despite its relatively smooth, flat surface, and
despite the absence of the spiral pumping grooves on the rotating
ring. The phenomenon of the fluid film rotating on and with a
smooth seal face results from a laminar flow, with the relative
flow being provided to the stationary liquid by the rotation of the
faces 42,62 of rings 40,60. As the fluid film meets the faces 42,62
of mating rings 40,60, the fluid film is constrained by the grooves
44, 74 and is forced radially inwardly along a surface boundary
layer on each face 42,62. Although each ring having the spiral
grooves is retained stationary, the action of the laminar flow is
sufficient to pump enough fluid between the faces and create the
gap between the faces during relative rotation between the
faces.
A biasing force is necessary to counteract the tendency to increase
the gap created by the fluid. If the gap becomes too great, the
leakage of fluid from the high pressure side of the seal becomes
excessive and needs to be brought under control. Referring again to
FIG. 1, a biasing force is provided to each of the primary rings
36,64 by a single set of plural springs 80 evenly disposed around
the circumference of the annular primary rings 36, 64. Springs 80
press directly onto a pair of discs 82,84 which abut the faces of
each primary ring 36,64, respectively, which faces are opposite the
sealing faces 42,62, respectively. Thus, the force of springs 80
counteracts the opening force of the spiral grooves while the
pressure forces acting on each of the rings 36,64 counteract each
other.
The springs 80 are held in place by a retainer 90 having a
cylindrical outer circumferential wall 92. The retainer 90 has an
elongated inner wall 94 defining an annular space which at one end
accommodates mating seal ring 40 of seal 22 and at the other end
accommodates mating seal ring 60 of seal 24.
Along a central portion of inner diameter wall 94, is an annular
disk element 96. In the preferred embodiment, the disk element 96
is integral with the retainer 90. Disk element 96 includes a
plurality of apertures 98 which extend therethrough. The apertures
98 have a sufficiently large diameter to permit insertion of the
springs 80 therethrough. The retainer 90 and disk element 96 thus
retain the springs 80 in both circumferential and radial positions.
Even spacing of the springs 80 around the circumference of disk
element 96 provides an even bias on the mating rings 40, 60 around
the full circumference of the rings 40,60. In the preferred
embodiment, there are four springs disposed at regular 90.degree.
intervals within the disk element.
The retainer 90 at an inner diameter of disk element 96 is adjacent
the thicker portion 50 of sleeve 48. A plurality of set screws (not
shown) extend radially through bores which are radially disposed in
the disk element separated from the axial apertures 98. The set
screws impinge on the outer circumferential surface of the sleeve,
whereby the retainer 90 becomes fixed in the axial and
circumferential directions relative to the sleeve 48. Thus, the
retainer 90, disk element 96, primary rings 36,64 and the springs
80, all rotate together with the shaft 16 during operation of the
device in which the seal arrangement is used.
The inner diameter of the cylindrical retainer 90 further includes
adjacent each end an internal groove 98 for receiving a snap ring
100. Each snap ring 100 fits within the groove 98 and provides a
radially extending wall 102. Wall 102 of one snap ring 100
interfaces with wall 37 of primary ring 36 to retain the ring
within the retainer 90. Similarly, wall 102 of the other snap ring
100 interfaces with the radially extending wall 72 of primary ring
64 to retain the ring within the retainer 90. Under normal
operating conditions, however, each primary ring is preloaded
during assembly so that the walls 37,72 of the respective primary
rings are separated from the snap ring walls 102.
As described above, a liner assembly 28 fits within the packing
housing formed by wall 12 and encloses a portion of the
arrangement, including seal 22 and a part of the retainer assembly
90. Liner assembly 28 comprises an inner diameter annular support
flange portion 110 which is shaped and configured around its inner
diameter to receive the mating ring 40 of seal 22. Radially
extending wall 39 of ring 36 closely abuts a corresponding radially
extending wall of the flange portion 110.
The flange portion 110 further includes a plurality of axially
extending pin receiving bores 112 for receiving pins 43 to provide
stationary engagement between the flange portion 110 and the mating
ring 40. An annular groove 114 provides a sealing receptacle for
receiving the O-ring 47 which seals between the liner assembly 28
and the primary ring 36.
An outer diameter flange portion 120 of liner assembly 28 is
attached to the inner diameter support flange portion 110 by an
elongated tubular portion 116. Tubular portion 116 has an outer
diameter that fits within the housing wall 12, but does not
necessarily seal against it. A fluid tight seal between liner
assembly 28 and housing 12 is provided by an O-ring 122 which fits
within a groove 124 in the outer diameter corner between the outer
diameter flange portion 120 and the tubular portion 116. Groove 124
has a diameter at one of its axially extending walls which is
identical to the outer diameter of the tubular portion 116, so that
it can be considered as an extension of the outer diameter wall of
tubular portion 116. In this position, when a radially extending
wall 126 of outer flange portion 120 is brought flush with the wall
of housing 12, the O-ring 122 is pressed against the housing wall
to seal between the liner assembly 28 and the housing 12. Sealing
load in the axial direction is preferable to that in the radial
direction because the liner can be more easily installed by sliding
the tubular portion with the packing housing.
The outer flange portion 120 preferably includes a connection to
the wall of housing 12, as will be described below. Several bolts
130, shown in phantom, extend through a set of equidistantly
disposed recessed bores 128, shown in phantom, in the radial wall
of the outer diameter flange portion 120 to connect the liner
assembly 28 to the flanged gland plate 30.
Gland plate 30 includes an inner diameter portion which has axially
extending inner diameter sealing surface 132 against which the
O-ring 75 is sealed. The depth of groove 77 which is disposed in
the outer circumferential diameter of mating ring 60 provides
enough clearance to enable the mating ring 60 to be press fitted
into the annular shoulder formed by surface 132. Together with the
O-ring 75, a fluid tight seal is effected between the mating ring
60 and the gland plate 30.
Gland plate 30 includes an inlet port 134 and a passageway 136 for
a fluid connection between the intermediate chamber 26 and the
inlet port 134. The inlet port 134 is itself connected to and in
fluid communication with a source of a gas which is non-hazardous
to the environment but which is compatible with use of a specific
process fluid. Any relatively inert gas, or a gas which is
non-reactive with the process fluid, may be utilized as a buffer
gas. Nitrogen gas is preferable as a relatively inert gas because
of its low cost and easy availability, but a noble gas, such as
argon, neon, or the like, may also be considered appropriate in
certain applications. In a limited number of other applications,
air may be used as the buffer fluid if its use is compatible with
the process fluid.
Alternatively, a gas that is reactive with the process fluid may
also be used in certain applications in which the reaction is
desirable, such as when the buffer gas is to be added to the
process fluid at some stage of the process fluid processing. As an
example, the introduction of carbon dioxide into the process fluid
may be performed as part of the chemical processing of the process
fluid. When used in this way, close measurement of the amount of
buffer fluid introduced into the process fluid is important, and a
calculation of the buffer fluid volume pumped into the process
fluid by the spiral grooves may be necessary to provide only that
amount of carbon dioxide which is necessary for the desired
chemical reaction to occur.
In the preferable environment, the buffer fluid gas is at a
pressure exceeding the maximum expected process fluid pressure.
Preferably, the source of nitrogen provides a nitrogen stream to
the inlet port 134 at about 10 p.s.i. above the maximum process
fluid pressure. The nitrogen source may be provided by any of a
number of possible means. For example, for an application in a
chemical plant, the nitrogen source may be a piped-in line of
nitrogen which results from by-products of various chemical process
and which is readily available throughout most chemical plants. The
pressure of the nitrogen supplied to the inlet port may be
regulated to the desired level between the line source and the
inlet port.
Alternately, the source may be a bottled nitrogen source at high
pressure which also requires a regulator for a supply of nitrogen
at the desired pressure. In the preferred embodiment, the inlet
port is disposed at the highest point of the gland plate 30 for
convenient access but this is not necessary for operation and in
other configurations, it may be desirable to provide an inlet port
at a different position and oriented at a different angle as befits
a particular application.
The collar 52 is axially disposed outside the immediate seal
arrangement and provides a connection between the sleeve 32 and the
shaft 16. The axial position of the sleeve 32 is important in
providing clearance of the axially movable elements in each seal.
To ensure that the sleeve is axially disposed at the proper
location, the collar in 52 is fit over the sleeve 32 and connected
thereto by set screws 140 shown in phantom. The set screws 140
extend through the sleeve 32 and into a predetermined axial bore
142 in the shaft 12, thereby connecting the three elements together
and axially fixing each relative to the other.
The proper spacing of the sleeve 32 relative to the gland plate 30
and to the other elements of the seals 22,24 is effected by use of
a plurality of spacers 144. Each spacer 144 is a right angled strip
with two legs, one leg being connected to collar 52 and the other
leg to gland plate 30 by cap screws (not shown) which extend in
threaded bores (not shown) appropriately disposed in the collar 52
and in the gland plate 30.
Spacer 144 is used only during assembly of the seal arrangement
onto the shaft 16, and is removed once that assembly is completed,
as is symbolized by the spaced apart spacer shown in phantom.
Nevertheless, it is shown as being connected in FIG. 1 to indicate
the relation between the seal arrangement elements. Removal of
spacer 144 after completion of assembly does not change the
relative positions of those elements.
The materials comprising specific elements are commercially
available and in most respects standard in the sealing industry. In
the preferred embodiment, each of the primary rings 36, 64 are
carbon graphite rings and the mating rings 40,60 are silicon
carbide or tungsten carbide. The spring 80 is stainless spring
steel and the liner, the gland plate 30, the sleeve 32, the collar
52, the spacer 144 and the various cap and set screws may all
comprise an appropriate steel, such as 316 stainless steel.
The O-rings which are exposed to a process fluid, which in most
cases is intended to be corrosive or toxic. Thus, the O-rings must
comprise a material which is relatively impervious or chemically
resistant to a majority of corrosive fluids. Accordingly, O-rings
47,56 and 58 comprise a chemically resistant elastomer, such as
perfluoroelastomer. The expense of this material precludes its
extensive use for all of the O-rings throughout the seal
arrangement. O-rings 70, 75 and 138 each may comprise an
elastomeric material which is generally used for O-rings, such as a
fluorocarbon elastomer, chloroprene, ethylene propylene or nitrile.
During normal operation of the seal arrangement, the O-rings 70, 75
and 138 are not exposed to the corrosive process fluid, and thus
there is no requirement of a chemically resistant or impervious
elastomeric material for those O-rings.
The assembly of the seal arrangement 10 must proceed in accordance
with a predetermined procedure. The preferable construction of the
seal arrangement 10 is as a cartridge permitting assembly of a
majority of the seal off-site from where the seal will be used.
Thus, the only on-site assembly which would be required in that
case would be the installation of the seal arrangement cartridge,
connecting the gland plate 30 to the housing 12 and adjusting the
axial position of the sleeve 32.
Assembly of the cartridge at an off-site manufacturing plant would
begin by disposing the disc 84 in one end of the retainer 90 and
sliding the disc toward the retainer central disk portion 96. The
O-ring 70 is then fit within the annular shoulder 84 of primary
ring 64 and the primary ring 64 is placed into the retainer 90 with
the face opposite the seal face 66 abutting the disc 84. Snap ring
100 is then disposed within groove 98 to retain the primary ring 64
within the retainer 90.
The next step is sliding the retainer 90 together with the primary
ring 64, the disc 84 and the O-ring 70 over a sleeve 32 from the
end with thinner portion 51 toward the thicker portion 50, until
the inner diameter of the disc 84, the O-ring 70 and the inner
diameter of the primary ring 64 engage the outer diameter of the
sleeve thicker portion 50.
The springs 80 are then placed in the appropriate bores 94, around
the retainer central disc portion 96 from the other end of the
retainer 90 so that the springs 80 engage the disc 84. Disc 82 is
then slid from the other end of the retainer 90 until the disc
contacts the spring 80. O-ring 58 is disposed within the outer
diameter groove of sleeve 32 and primary ring 36 is inserted within
the opposite end of the retainer 90 so that the back face, opposite
from sealing face 38 contacts the disc 82. Care must be taken in
the insertion of primary ring 36 so as to avoid squeezing or
catching an inner diameter corner of the ring 36 on the O-ring
58.
After the back face of the primary ring 36 clears the O-ring 58,
the primary ring 36 and disc 82 compress the springs 80 to some
extent. A second snap ring 100 is fit within the groove 98 at the
opposite end from the first snap ring, thus retaining both primary
rings 36,64 within the retainer 90. The springs 80 will bias the
primary rings 36, 64 outwardly until the respective shoulders 72,37
engage the snap rings 100.
The thicker portion 50 of sleeve 32 is then axially centered within
the space defined by the primary rings 36,64 and a plurality of set
screws (not shown) is inserted in equidistantly disposed radial
bores (not shown) both in the retainer center disk portion 96 and
the sleeve thicker portion 50 to connect the retainer 90 to the
sleeve 48 and to fix the retainer 90 in the axial and
circumferential directions for rotation with the sleeve. The O-ring
56 can be inserted into the inner groove of sleeve 32 at any time
when convenient.
The liner assembly 28 together with retaining pin 43, which during
manufacture has been press fit within the bore 112 of the liner
assembly inner diameter portion 110, is brought up. O-ring 47 is
fit within groove 114 and the mating ring 40 is inserted into the
liner assembly so that the non-sealing faces on the opposite side
of mating ring 40 from the face 42 engage the liner assembly inner
diameter portion 110 and the pin 43 is inserted within the bore 41
of mating ring 40. Care must be taken to ensure that the O-ring 45
does not interfere with the insertion of the mating ring 40.
The next assembly step is fitting O-ring 75 around the outer
circumferential groove 77 of mating ring 60, and fitting the mating
ring 60 within the gland plate 30 so that the outer circumferential
surface of mating ring 60 engages the surface 132 of the gland
plate 30. An O-ring 138 is disposed in the groove 139 of the gland
plate.
The retainer 90 together with all of the appurtenant elements
including primary rings 36, 64 and sleeve 32 is then positioned
within the liner assembly 28 so that the sealing face 42 of the
mating ring 40 engages the sealing face 38 of primary ring 36. The
gland plate 30, together with the mating ring 60 is then slid over
the thinner portion 51 of sleeve 32 until the sealing faces 62 and
66 engage.
The thicker portion 50 of sleeve 32 is then axially centered within
the space defined by the primary rings 36, 64 and a plurality of
set screws (now shown) is inserted in equidistantly disposed bores
(not shown) both in the retainer center disc portion 96 and the
sleeve thicker portion 50 to connect the retainer 90 to the sleeve
32 and to fix the retainer 90 in the axial and circumferential
directions for rotation with the sleeve. The O-ring 56 can be
inserted into the inner groove of sleeve 32 at any time when
convenient.
A gap should become apparent between the liner assembly outer
diameter flange portion 120 and the gland plate 30 which results
from the springs 80 being in an extended condition, thus biasing
the primary rings 36, 64 to the limit of the retainer position
permitted by snap rings 100. The gland plate 30 is then positioned
relative to the bores of the outer diameter flange portion 120 to
maintain alignment for insertion of the bolts 148 which will
connect the assembly to the housing 12. The gland plate 30 is then
depressed in the axial direction thus pushing towards each other
the primary rings 36, 64 while compressing the springs 80.
Insertion and tightening of bolts 130 connects the liner assembly
28 to the gland plate 30, and defines the position of the primary
rings 36, 64 within the two mating seal faces 42,62. However, the
sleeve 32 together with the retainer 90, are axially slidable
relative to the position of the primary rings 36, 64.
Once the bolts 130 are tightened and the gland plate 30 is
connected to the outer diameter flange portion 120 of liner
assembly 28, the seal arrangement 10 is ready for installation on
to a shaft 16. A set of spacers 144 is first connected to the outer
radial wall of the gland plate at an appropriate radius from the
center line by screwing cap screws (not shown) through the radially
extending leg of each spacer 144 into the bores in the gland plate
30. The collar 52 is then slipped into the space defined by the
other, axially extending leg of each spacer 144 and cap screws
attach the spacers 144 to the collar 52. The seal arrangement can
then be shipped to an installation site.
A repeller pump (not shown) may be considered as an appropriate
example for installation of the seal arrangement. The motor of such
a pump (not shown) which would be connected to the shaft 16 at the
right side of FIG. 1, would first be disconnected. Any material,
such as old packing, would be withdrawn from the stuffing box
defined by housing 12, and the surfaces of the shaft, stuffing box
and wall 12 would be cleaned of debris or corrosion, if necessary.
The seal arrangement, as a cartridge would then be carefully
inserted so that the outer diameter wall of the liner assembly
inner diameter portion 110 fit within the stuffing box defined by
the wall of housing 12, while simultaneously the sleeve 32 fit over
the shaft 16. Care must be taken to ensure that the O-ring 56 does
not interfere with the slidability of sleeve 32 along the shaft
16.
The seal arrangement cartridge 10 is then slid along the shaft 16
until the radial wall 126 of the liner assembly outer diameter
flange portion 120 engages the radial wall of housing 12 while
simultaneously compressing O-ring 122 to effect a seal
therebetween.
Bolts 148 are then inserted into the appropriate bores through the
gland plate 30 and liner assembly outer diameter flange portion 120
and screwed into the threaded bore 150 in the radial wall of
housing 12. The bolts 148 fix the stationary portions of the seal
arrangement cartridge 10 relative to the housing 12; while the
sleeve assembly 32, together with the retainer 90 and primary rings
36, 64, are free to move axially and to rotate with the shaft.
Axial centering of the sleeve assembly 32 is once again performed
by the spacers 144 fixing the position of the sleeve assembly 32
and of the retainer 90 which is connected to the sleeve 48. The
spacers 144 position the bores 142 through which at the appropriate
axial position relative to the shaft 16 so that a small rotation of
the shaft 16 disposes the bores 142 of the collar 52 over threaded
bores 146 in shaft 16. Set screws 140 are then inserted through the
bores 142 of collar 52 and bores 143 in sleeve thinner portion 150
and screwed into the threaded bores 146, thus fixing the position
of collar 52 and sleeve assembly 32 relative to the shaft 16.
Spacers 144 are then removed by unscrewing the cap screws (not
shown) so that the shaft is free to rotate relative to the
housing.
Operation of the seal arrangement 10 requires the user to provide a
source of a relatively insert gas, such as nitrogen or one of the
noble gases, as a buffer fluid. The gas should be supplied at a
pressure which exceeds the maximum process fluid pressure by at
least 10 p.s.i. The buffer gas pressure may exceed the maximum
process fluid pressure by a much greater amount, in which case a
regulator may be necessary to decrease the pressure to a desirable
level. The supply of the buffer gas is continuously injected into
the inlet port 134 and the gas then enters the intermediate chamber
26 through the connecting passage 136.
During shaft rotation, the assembly comprising the retainer 90, the
primary rings 36, 64 and the sleeve 32 rotates with the shaft 16.
The only point of direct interface between the rotating elements
and the stationary elements, fixed relative to the housing 12, is
at the interface between the seal faces 38,42 and 62,66 of each of
the respective seals 22,24. That is, while the mating ring seal
faces 42,62 remain stationary, the primary ring faces 38,66 are
rotating relative thereto.
Introduction of a steady stream of a buffer gas into the
intermediate chamber 26 at a pressure exceeding both the maximum
process fluid pressure within the housing and the pressure in
ambient environment external to the housing, usually atmospheric
pressure, forces the buffer gas into and through the gap formed by
the seal faces during shaft rotation. Thus, the only leakage across
the seal faces 38,42 of seal 22 is the buffer gas leakage from the
intermediate chamber 26 into the housing chamber 18, and across the
seal faces 62,66 of seal 24 is from the intermediate chamber 26
into the ambient environment, such as atmosphere 20.
Actual contact between the seal faces is to be avoided during the
rotation of the shaft, but the gap which develops between the seal
faces is small enough to maintain only slight leakage of the buffer
fluid through each of the seals 22,24. The direct interface between
the two sets of seal faces maintains the sealing capacity of one
seal between the process fluid contained by the housing and the
intermediate chamber and the other seal being between the
intermediate chamber and the ambient environment external to the
housing.
In the preferred embodiment, the spiral grooves 44 on the mating
ring seal face 42 also pump the buffer gas from the intermediate
chamber 26 and into the process fluid chamber 18. Ideally, the
pumping action of the spiral grooves 44 and the buffer gas pressure
act in concert to maintain all leakage across the seal 22 in the
desired direction and to inhibit the escape of toxic or corrosive
process fluids into the intermediate chamber 26. Moreover, even if
some process fluid does leak into the intermediate chamber by
accident, the positive pressure of the buffer gas in the other
direction would tend to inject the process fluid back into the
chamber 18.
The configuration of the seal system together with the positive
buffer gas pressure prevents most leakage of the process fluid to
atmosphere. A failure of one of the seals would not permit process
fluid leakage, because continuous monitoring of the gas pressure in
the intermediate chamber 26 would signal the need for a system
shutdown in the event that the pressure dropped below a
predetermined level. For example, if one of the seals 22, 24
failed, then there would be an immediate pressure drop in the
intermediate chamber, which would cause the system to shut down and
a cessation of the rotation of the shaft 16. If it was seal 22
which failed, system shutdown would not permit escape of the
process fluid from the intermediate chamber 26 because of the
static seal provided by dam 76 of the seal ring face 62.
Conversely, if seal 24 failed, the static seal provided by dam 46
of seal ring face 42 would prevent process fluid from entering the
intermediate chamber, thus permitting only buffer gas to escape
from the intermediate chamber.
The advantages provided by the use of the inventive seal
arrangement include the elimination of a "wet" buffer fluid such as
oil, which can become messy and may contaminate the process fluid.
Moreover, oil lubricant is expensive.
In contradistinction, the preferred embodiment of the present
application is a dry running seal which has a gas as a lubricant.
When equipped with spiral grooves, the seal faces separate to
create a gap between the faces and the use of non-contacting type
seals results in longer seal life and reduces heat generation
resulting from contacting friction. A slight but steady stream of
the buffer gas through and across the seal faces acts as a coolant
to remove any heat which may be generated by viscous shear between
the seal faces. Thus, it is not necessary to circulate the buffer
fluid around the seal area since no frictional heat problem
arises.
For use with toxic process fluids, use of nitrogen as a buffer gas
is approved by environmental regulations and agencies. Moreover,
because seal failure will immediately shut down the system, the
seal arrangement according to the present invention can be used
without constant monitoring of gas effluent for toxic fluid
escape.
The inventive seal arrangement is capable of use in a variety of
sealing applications, including most pumps. For example, the seal
can be used with repeller pumps which evacuate the space in the
housing immediately around the seal rings so as to provide at least
a partial vacuum. Nitrogen "consumption", i.e. nitrogen injection
into the housing chamber, is reduced in a repeller pump because the
partial vacuum caused by the repeller permits a lower nitrogen gas
buffer pressure. It is nevertheless preferable to maintain a
pressure differential between the repeller chamber and the
intermediate chamber at about 10 p.s.i.
Whereas a preferred form of the invention has been shown and
described, it will be realized that alterations may be made thereto
without departing from the scope of the following claims.
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